Scientists searching for a way to delay the aging process may have found it in an intervention that many Americans battle with again and again—cutting calories. When used as a lifestyle choice, calorie restriction yields a significantly healthier and prolonged life.

Calorie restriction (CR)—under nutrition without malnutrition—is the only intervention that has been documented in laboratory animals to increase the average life span, or the average number of years an animal is expected to live, and maximum life span—the maximum number of years a species can possibly reach.

Researchers began studying the effects of reducing calories by 30 to 40 percent in young laboratory mice and rats nearly 60 years ago. They discovered that the rodent lifespan was increased by 50 percent and the onset of age-related disease was delayed. The National Institute on Aging has been investigating the impact of CR on the aging process in rhesus and squirrel monkeys since the late 1980s.

Study findings show that monkeys fed a calorie-restricted diet are aging at a slower rate over time and are healthier than their well-fed counterparts, according to George Roth, CEO of Geroscience, Inc. in Baltimore, and a former NIA researcher who has led many CR studies. The mortality rate also appears to be lower, but the outcomes are not yet statistically significant.

“The biological markers that normally change with age either change more slowly or don’t start changing until a bit later in life,” Roth said. “The most robust effect of CR is increased sensitivity to insulin and decreased insulin levels that CR will elicit fairly quickly in just about every species that has been studied.”

It has long been thought that CR is only effective when started at a young age. However, new research at the University of California, Riverside, found that restricting calories in mice the age equivalent of 65 in human years slowed the aging process and extended life by about 42 percent. This study suggests that CR can be beneficial even late in life, Roth said.

Human Studies Begin

Preliminary findings of the first-ever randomized human trial for calorie restriction showed promise in reducing age-related chronic diseases, such as heart disease, hypertension, and type 2 diabetes. Researchers at the Pennington Biomedical Research Center studied 48 adults, ages 25 to 50, with body mass index (BMI) measurements from 25 to 30. The CR group followed a nutritionally dense, 25 percent reduced-calorie diet for six months.

A second group followed a 12-1/2 percent restricted diet and increased their physical activity to burn another 12-1/2 percent of calories consumed. All participants received two meals a day at the center for the first three months.

The two CR groups lost an average of 10 percent of their weight after six months, according to the study principal investigator and professor, Eric Ravussin. Results also showed an improvement in insulin sensitivity and in the lipid profiles, a series of blood tests that indicate risk for heart disease and stroke.

As the researchers hypothesized, preliminary data suggest less DNA damage from oxidative stress. CR decreases metabolism, and therefore, decreases the production of reactive oxygen processes that produce free-radicals and other damaging effects.

“The importance of these studies is that they are the first attempt in humans to see if CR can make a difference, Ravussin said. “Of course, in the studies done in flies, worms, rodents, and now monkeys, the ultimate end point is mortality. But I doubt mortality will ever be studied in human populations. Having the biomarkers of aging and seeing that you can reverse them by CR would be very important.”

Body temperature and insulin levels are considered biomarkers of aging since they increase over time. The calorie-restricted participants showed a significant decrease in body temperature and in insulin levels, suggesting that the process of aging has slowed.

But how did participants respond to calorie restriction? Surprisingly well, Ravussin said. Compliance was high as indicated by the weight loss, due to careful screening of participants prior to the study. The participants’ quality of life was not decreased by the strict diet regimen.

“There is always the question of, you may live longer, but it seems longer when you are calorie deprived,” he said. “But, people were quite thrilled. One of the reasons was, with the BMIs at 25 to 30, some people were slightly chubby to begin with, and they were very happy with the weight loss.”

Calorie restriction may not be feasible for the general population since our environment is not conducive to this practice, Ravussin said. The second phase of his study will require a two-year commitment to CR. People must be willing to change their lifestyle long-term to sacrifice calories for health advantages and a potentially longer life.

A Lifestyle Choice

Living the CR lifestyle doesn’t have to mean reducing calories by the maximum amount. Even slight calorie reduction has its benefits, as most dieters discover when they lose weight. While it would be extremely difficult for most people to reduce calories by 40 or 50 percent, many find that restricting intake by 10 to 30 percent is not too painful, said Brian M. Delaney, president of the Calorie Restriction Society, which has nearly 2,000 members.

The motivation to restrict intake for years divides the membership into two categories. Many of the youngest members – those in their 20s, 30s, and early 40s—are life extensionists who hope to experience a prolonged life. The second group, made up of members in their 50s and 60s, cut food intake to prevent or delay many chronic conditions associated with aging.

“The second group is really not interested in slowing the aging process. They don’t want to live to 120 or 130; they just don’t want to get a heart attack at age 60,” Delaney said.

A majority of the members report that the effects from CR are overwhelmingly positive—except that they are hungry. Some claim that eating bulky, low-cal foods, such as vegetables, can minimize hunger pangs. Many members eat breakfast, but skip lunch so that their hunger is focused in the late afternoon before dinner.

Delaney recommended visiting your health care provider and taking medical tests, such as fasting glucose, cholesterol levels, and other markers of disease. Try a mild or moderate version of the diet for three to six months, then take the medical tests again and compare the results.

A Magic Pill

Those of us who are too attached to our hearty food portions to try CR may find comfort in the fact that on the horizon are pharmaceuticals or nutritional supplements, called CR mimetics, which will provide many of the same health benefits of CR without the hunger. Many products available today claim to affect one biomarker of aging, such as increasing DHEA levels or decreasing the damage of free-radicals. Commercial, government, and academic laboratories are racing to discover a product that will have the maximal effect on health and aging.

“The holy grail of biogerontology right now is to come up with these CR mimetics,” Roth said. “Most of the products on the market are considered segmental CR mimetics because I don’t think anybody has a product or an approach that will mimic CR 100 percent. I envision—if we get past many legal barriers— ultimately a ‘cocktail’, whereby several of the CR candidates could be incorporated into a supplement or drug.”

Popping a health-promoting, age-slowing pill would be more practical for most people than following a rigorous regimen of calorie restriction every day for a lifetime, he said.